1. Field of the Invention
The present invention relates to a method for manufacturing an SiC semiconductor device, and more particularly to a method for manufacturing an SiC semiconductor device that allows the measurement of resistance by a four-point probe method.
2. Description of the Background Art
An activation annealing apparatus used in manufacturing processes of a silicon carbide (SiC) semiconductor device performs annealing at a temperature of 1600° C. or higher. In conventional silicon (Si) semiconductor devices, an annealing temperature is up to approximately 1300° C. A thermocouple (for example, JIS-standard R-type or B-type thermocouple) is inserted inside heat treatment equipment to perform temperature calibration.
When heat treatment is performed at a high temperature of 1600° C. or higher using the activation annealing apparatus, a thermocouple made of a tungsten-rhenium (W—Re) alloy can be used to perform temperature calibration, but oxidation of the thermocouple deteriorates wires of thermocouple. Therefore, since the deterioration will break the wires of thermocouple when the thermocouple is inserted twice or so in a high-temperature atmosphere, it is very difficult to steadily control the temperature calibration of the activation annealing apparatus.
Under the method using the thermocouple, a temperature distribution in a substrate surface will be measured with a substrate having the thermocouple. However, a method for welding wires of the thermocouple onto an SiC substrate also has many problems, and it is difficult to control and operate the method. Accordingly, in the current operation, a method is used to fabricate a simple patterned substrate using an SiC substrate, to calculate acceptor concentration in the substrate by measuring a C-V characteristic (capacitance-voltage characteristic) of the substrate, and to substitute for a temperature equivalent. The above-mentioned simple patterned substrate is manufactured in accordance with the following processes.
First, aluminum (Al) is implanted into the SiC substrate in order to form a p-type layer in a substrate surface layer. Next, a protective film (for example, a graphite film) is formed on the substrate surface as a pretreatment of the annealing. Then, the annealing is performed at a high temperature of 1600° C. or higher by the activation annealing apparatus in order to activate the implanted impurity. Subsequently, the protective film is removed and a cylindrical Al electrode is formed on the SiC substrate surface. Refer, for example, to Japanese Patent Application Laid-Open No. 2012-231037 and Japanese Patent Application Laid-Open No. 2012-248648 for impurity implantation into the SiC substrate, annealing, and the like.
C-V measurement is performed on the SiC substrate formed through the above processes. Al acceptor concentration in the substrate is calculated. Temperature calibration is performed by converting this Al acceptor concentration into temperature.
The above-described manufacturing processes of the simple patterned substrate applied to the method for manufacturing the conventional SiC semiconductor devices have a problem that the number of manufacturing processes increases because many other processes are also included, such as Al electrode formation and patterning.
In addition, since the measurement in the substrate surface can be performed only at a point where an electrode is formed and the measurement cannot be performed at a point without an electrode, measurement points are limited. It is not possible to perform a detailed distributive analysis of the temperature in the surface.
If measurement with a four-point probe sheet resistance measuring instrument employed in heat treatment equipment for Si devices can also be performed on the SiC substrate as a substitute for this monitoring method, it is not necessary to form an Al electrode, and it is possible to measure at any point on the substrate. However, the SiC substrate itself is too hard to make contact with a probe, so that it is impossible to perform the measurement.